All publications cited in this application are herein incorporated by reference.
When plants are exposed to conditions where reduced water content in the soil due to a shortage of rainfall or irrigation leads to impaired water absorption, what could be called drought stress conditions, physiological functions of cells may deteriorate and thus various disorders may arise in the plant. When subjected to such stress factors plants display a variety of mechanistic responses as protective measures, with a resultant adverse effect on growth, development, and productivity. Significant losses in quality and yield are commonly observed.
While it has been known that phytohormones and some chemical substances such as plant growth regulators have effects on plants in reducing water stress such as drought stress or excessive moisture stress (see Journal of Plant Growth Regulation (2010) 29: 366-374), those effects are not necessarily satisfactory in practice. For example, organic osmolytes are small solutes used by cells of numerous water-stressed organisms and tissues to maintain cell volume. Similar compounds are accumulated by some organisms in anhydrobiotic, thermal and possibly pressure stresses. These solutes are amino acids and derivatives, polyols and sugars, methylamines, methylsulfonium compounds and urea. Except for urea, they are often called “compatible solutes”, a term indicating lack of perturbing effects on cellular macromolecules and implying interchangeability. However, these features may not always exist, and the practical use cannot be taken for granted since high levels might cause overstabilization of proteins and some protective properties of osmolytes are harmful in the absence of a perturbant to offset (Yancey, P. H. (2005). J. Exp. Biol. 208 (Pt 15): 2819-30). For example the osmolite glycinebetaine (betaine) affords osmoprotection in bacteria, plants and animals, and protects cell components against harsh conditions in vitro, however, engineering of betaine production in three diverse species lacking it, Arabidopsis, Brassica napus, and tobacco (Nicotiana tabacum), by constitutive expression of a bacterial choline oxidase gene only conferred a moderate stress tolerance in some but not all betaine-producing transgenic lines and the responses to stresses such as salinity, drought, and freezing were variable among the three species. Furthermore, a fitness cost was observed in the three species (Jun H., Hariji et al. (2000) Plant Physiol. 122: 747-56).
The foregoing examples of related art and limitations related therewith are intended to be illustrative and not exclusive, and they do not imply any limitations on the inventions described herein. Other limitations of the related art will become apparent to those skilled in the art upon a reading of the specification and a study of the drawings.